Research

Gen-2 Open-Access Wideband Full-Duplex Radios in COSMOS

In order to support experimentation with wideband full-duplex (FD) wireless, we integrated the FlexICoN Gen-2 open-access wideband FD radios with the city-scale PAWR COSMOS testbed. Each Gen-2 FD radio consists of an antenna, a customized Gen-2 RF self-interference (SI) canceller, a USRP software-defined radio (SDR), and a compute node.

The Gen-2 FD radio achieves enhanced RF SI cancellation performance and bandwidth based on the technique of frequency-domain equalization (FDE) [5], which is more suitable for compact and IC-based implementations. In order to support the integration with an SDR and to facilitate experimentation in a testbed with several nodes, we designed and implemented a Gen-2 wideband FDE-based RF canceller on a printed circuit board (PCB), which is an improved version of the Gen-1 narrowband RF canceller. In particular, the Gen-2 canceller includes two cancellation paths that can be selected through an RF switch: the Gen-1 (narrowband) path and the FDE (wideband) path.

The PCB design of the FDE-based RF canceller is available below. A preliminary version of the system with this PCB canceller was presented in [4]. A detailed discussion and system- and network-level evaluation of the canceller are available in [1, 2]. The details about the integration of the Gen-2 FD radios in the COSMOS testbed is available in [3]. We are working on integrating more cancellers and providing more advanced example experiments at different layers of the network stacks (PHY, Link, and above). Detailed tutorials and demos can be found here.

Figure 1. Gen-2 FD canceller board. (a) The implemented Gen-2 RF canceller consisting of a wideband frequency-domain equalization (FDE) path and a narrowband path, (b) the measured TX/RX isolation of the Gen-2 RF canceller without turning on the canceller, and with the narrowband (Gen-1)/wideband (FDE) path on, when the circulator antenna port is terminated by 50 ohm (left) and connected to an antenna (right), and (c) the implemented open-access Gen-2 wideband FD radios integrated in the COSMOS sandbox.

Please email Tingjun Chen (tingjun [at] ee.columbia.edu) if you use (or plan to use) the design of the FDE-based PCB canceller, or if you have any questions. We are currently working on an improved version of the PCB canceller and the design will be made available soon.